1. Field of the Invention
The present invention relates generally to a packet data service, and more particularly to a method by which a user equipment located in a geographical area including a plurality of overlapping cells having different frequency bands can receive packet data of a packet data service provided to at least one cell selected from the plurality of cells in the geographical area.
2. Description of the Related Art
FIG. 1 is a block diagram schematically illustrating a conventional mobile communication system. In FIG. 1, the mobile communication system is a universal mobile terrestrial system (UMTS) mobile communication system that includes a core network (CN) 100, multiple radio network subsystems (RNSs) 110 and 120, and a user element (UE) 130. Each of the RNSs 110 and 120 includes a radio network controller (RNC) and multiple base stations (or node Bs). For example, the RNS 110 includes a RNC 111, and node Bs 113 and 115, and the RNS 120 includes a RNC 112, and node Bs 114 and 116.
Further, each of the RNCs 111 and 112 may be classified as a serving RNC (SRNC), a drift RNC (DRNC), or a controlling RNC (CRNC) according to an operation of each RNC. The SRNC is an RNC for managing information of each UE and controlling data transmission with the CN 100. Further, when data of a UE is transmitted/received to/from a SRNC via another RNC other than the SRNC, the DRNC becomes the another RNC.
The CRNC is an RNC for controlling each node B. When the RNC 111 manages the information of the UE 130 as illustrated in FIG. 1, the RNC 111 operates as a SRNC with respect to the UE 130. Further, when the UE 130 moves and the data of the UE 130 is transceived through the RNC 112, the RNC 112 becomes a DRNC with respect to the UE 130, and the RNC 111 controlling the node B 113 communicating with the UE 130 becomes a CRNC of the node B 113.
The RNC and the node B are connected to each other through a lub interface. The RNCs are connected to each other through a lur interface. The UE and a UTRAN are connected to each other through a Uu interface.
The RNC assigns a radio resource to multiple node Bs controlled by the RNC and the node B provides the UE with the radio resource assigned by the RNC. The radio resource is provided according to each cell, and the radio resource provided by the node B represents a radio resource regarding a specific cell controlled by the node B.
The UE sets a radio channel by means of the radio resource regarding the specific cell controlled by the node B, and transmits/receives data by means of the set radio channel. Accordingly, because the UE recognizes only a physical channel provided according to each cell, a distinction between a node B and a cell has no meaning. Hereinafter, the present invention uses the terms a node B and a cell interchangeably.
In order to support multicasting multimedia communication, a broadcastlmulticast service provides a service from one data source to a plurality of user equipments (UEs). The broadcast/multicast service may be classified as a cell broadcast service (CBS), a message-centered service, and a multimedia broadcast/multicast service (MBMS) supporting a multimedia such as a real-time image and voice, a still image, characters, etc.
FIG. 2 is a block diagram schematically illustrating a network for providing the MBMS service in the mobile communication system. Referring to FIG. 2, a broadcast/multicast-service center (BM-SC) 210 provides an MBMS stream, and schedules a stream for the MBMS service to transmit the stream to a transit network 220. The transit network 220 is a network located between the BM-SC 210 and a serving GPRS support node (SGSN) 230 and sends the stream for the MBMS service, which is received from the BM-SC 210, to the SGSN 230. Herein, it is assumed that the SGSN 230 may include a gateway GPRS support node (GGSN) and an external network, etc., and that there are multiple UEs intending to receive the MBMS service at a predetermined time point, e.g., a UE 261, a UE 262, and a UE 263, each belonging to a first cell (node B1) 260, and a UE 271 and a UE 272, each belonging to a second cell (node B2) 270.
The SGSN 230 having received the stream for the MBMS service from the transit network 220 controls an MBMS related service of UEs intended for reception of a MBMS service. For example, the SGSN 230 manages MBMS service accounting related data of each UE and selectively transmits MBMS service data to a specific RNC 240. Further, the SGSN 230 creates and manages an SGSN service context for the MBMS service X, and transmits the stream for the MBMS service to the RNC 240 again.
The RNC 240 controls a plurality of node Bs and transmits the MBMS service data to a node B, which includes a UE requesting the MBMS service, from among the node Bs controlled by the RNC 240, controls a radio channel set for providing the MBMS service, and creates and manages a RNC service context for the MBMS service X with the stream for the MBMS service received from the SGSN 230. Further, as illustrated in FIG. 2, only one radio channel is assigned to one node B, e.g., a Node B 260 and UEs 261 to 263, in order to provide the MBMS service. Further, a home location register (HLR) is connected to the SGSN 230 to perform an subscriber authentication for the MBMS service.
FIG. 3 is a view illustrating a process through which the MBMS service is provided between a RNC and a UE requesting the MBMS service. The RNC provides the MBMS service to corresponding UEs requesting the MBMS service via a node B. Herein, it is clear that the MBMS service is performed via a node B. Further, a MBMS control message transmitted for the MBMS service will also be described.
Referring to FIG. 3, a UE 300 is a UE intended for reception of the corresponding MBMS service and an RNC 302 is RNC transmitting the MBMS service. Four steps are sequentially performed in a sequence of an announcement step, a joining step, a notification step, and a radio bearer (RB) setup step. Hereinafter, the four steps will be described with reference to FIG. 3.
In step 331, i.e., the announcement step, an SGSN 304 informs the UE 300 of a start time of the MBMS service. Herein, the information contains the kinds of MBMS services, time information on a start of the MBMS services, and duration of the MBMS services.
In step 341, the UE 300 requesting the MBMS services performs the joining step for the SGSN 304 according to the MBMS service notification by the SGSN 304. In the joining step, the UE 300 transmits a joining request message requesting a joining to the SGSN 304. The joining request message includes the identification code of a specific MBMS service, which is requested by the UE 300, and the identifier (UE ID) of the UE 300 requesting the MBMS service from among a MBMS service list transmitted from the SGSN 304.
Further, in step 341, the SGSN 304 performs an authentication process for the UE 300 requesting the MBMS service, and notifies the UE 300 of information regarding whether or not the UE 300 can receive the MBMS service from the result of the authentication. The SGSN 304 stores a list of UEs intended for reception of the specific MBMS service and the positions of the UEs by performing step 341.
In the mobile communication system, when the joining step for the MBMS service has been completed, the notification step, which is illustrated in steps 351, 352, and 361, is performed. More specifically, when a BM-SC reports the start of the MBMS service, the SGSN 304 transmits a session start message to the RNC 302 including the UE 300 having performed the joining process, in step 351. In step 352, the RNC 302 transmits a notification message for paging the UE 300, which is to receive the MBMS service, by means of a common channel, such as a secondary-common control channel (S-CCPCH). The notification is a process through which the SGSN informs the corresponding UE 300 requesting the MBMS service of the start of the MBMS service. Because a plurality of UEs are paged through the transmission of the notification message, step 352 is called a group paging step for the distinction with the existing paging procedure. For example, the notification message can be transmitted through a MBMS control channel (MCCH).
In step 361, the UE 300 paged in step 352 transmits a response message for the notification message. Through the transmission of the response message, the RNC 302 can check the number of UEs intended for reception of the MBMS service according to cells, and determine the kind of radio channels of a corresponding cell. The RNC 302 does not count all UEs intended for reception of the MBMS service. Instead, the RNC 302 counts the UEs only until the number of the UEs can satisfy a threshold for channel type decision. When a plurality of UEs contained in a specific cell intend to receive a MBMS service, the RNC 302 provides the MBMS service through a common channel. However, when a cell contains a small number of UEs intended for reception of the MBMS service, the RNC 302 can assign a dedicated channel according to each UE and provide the MBMS service.
In step 371, the UE 300 requesting the MBMS service and performing the step relating to the notification performs the radio bearer setup step by means of radio bearer information transmitted by the RNC 302 through an MCCH. The radio bearer setup step is a step in which a radio resource is actually assigned in order to provide the MBMS service and in which information on the radio resource is announced to relating devices. Further, in the radio bearer setup step, MBMS radio bearer information enabling the MBMS service to be received without an error is transmitted. That is, the UE 300 can restore the transmitted MBMS service without an error by using the MBMS radio bearer information. The MBMS radio bearer information may include radio channel information such as OVSF code information, transmission format information, radio link control (RLC) information, packet data convergence protocol (PDCP) information, etc. A detailed description about the information is disclosed in a 3GPP TS 26.331.
When the radio bearer setup step has been completed, all UEs intended for reception of a specific MBMS service recognize information on a radio link through which the MBMS service is provided and information on an upper layer in which the MBMS service is processed.
In step 381, when the RNC 302 transmits MBMS data transmitted from the SGSN 304 through a set MBMS RB, the UE 300 receives the MBMS data provided through the MBMS RB.
As indicated above, the MCCH is a channel through which control information on the MBMS is provided. Specific characteristics of this channel are currently being discussed and have not been standardized yet. According to recent discussions, an MCCH is expected to have the following characteristics:
1. one MCCH is constructed per cell;
2. an MCCH is transmitted thorough a common physical channel such as an S-CCPCH; and
3. UEs can obtain information on an MCCH assigned according to each cell as system information.
FIG. 4 illustrates a structure in which a plurality of frequency areas (FAs) overlap in one area. As illustrated in FIG. 4, one RNC includes at least one FA and a plurality of FAs can perform a MBMS service in the same area. That is, in servicing the same MBMS data in the same area, radio resources that are different from each other are used.
More specifically, FIG. 4 illustrates four FAs, that is, FAs 401 to 404. The four FAs service one MBMS data with respect to the same area. A UE contained in one of the four FAs can receive MBMS data transmitted from the FA including the UE. That is, the area is a single area in view of geographical concept, but the area includes four cells having different frequencies in view of FA supporting the MBMS data.
It is assumed that a plurality of FAs overlap in the aforementioned one area and each of the FAs services the same MBMS data to at least one UE. Herein, a plurality of radio resources are used for the same MBMS data, thereby wasting the radio resources.
Accordingly, when multiple FAs overlap in one area, at least one FA of the FAs is selected and MBMS data can be provided. Further, when the MBMS service is impossible in a specific FA having multiple overlapping FAs using one area, there is a problem in that the UE contained in the FA in which the MBMS service is impossible cannot receive the MBMS service.
Referring to FIG. 4, when only the FA 402 can support the MBMS service and the FAs 401, 403, and 404 do not support the MBMS service, the UEs contained in the FAs 401, 403, and 404 cannot receive the MBMS service. Accordingly, a method is necessary, which enables even a UE contained an FA that does not support the MBMS service to receive the MBMS service.